Once your map has been saved, it is stored in your ArcGIS Online account and can be made available to viewers over the Internet.
By selecting the share feature, ArcGIS Online will assist you in making your map available to others. With this feature, you can decide who is able to view your map (public or members of a created group). In addition, you can share a link to your map or embed your project in a webpage, Facebook, Twitter or a web application. ArcGIS Online will guide you through the process for sharing with each method.